In the manufacture of plastic sheet or film materials, such as polyethylene, polyvinyl chloride, and polystyrene, both in dense form and foam form, the material is sometimes extruded in the form of a bubble or circular tube and moved away from the extruder a distance necessary to cool and cure the product. The bubble can be treated in various ways to form various products. For instance, the bubble can be slit along its length, spread flat and rolled into a reel, or the bubble can be flattened, rolled into a reel or bags can be formed, or the bubble can be flattened and its edges trimmed to form two or more separate sheets, and the separate sheets can be accumulated in separate rolls.
The material produced from trimming the plastic material is scrap and must be disposed of or possibly recycled with the virgin plastic or base material, and additives such as a color additive. Scrap is also generated by producing unacceptable rolls and unacceptable other finished products such as bags, etc. It is highly desirable to recycle the scrap material, since it is difficult to dispose of and costly to reclaim in a separate operation. The recycling of the scrap material, therefore, helps to reduce the cost of manufacturing the product.
While various scrap recovery systems have been developed in the past for recycling the scrap plastic material with the base material through the process machine such as an extruder, the previous systems have been costly and erratic in operation. They do not function to feed the mixture of scrap material and base material in a uniform mixture to the process machine. The base material fed to the process machine usually is more dense than the scrap material so that when the base and scrap material are placed in a common supply container, the base material tends to migrate toward the lower portion of the container while the scrap material tends to float on the base material. This causes the base material to be fed from the lower outlet opening of the supply container to the extruder while the scrap material accumulates in the container. The scrap material is later fed to the extruder in large quantities which creates undesirable results such as an inconsistency in the extruded product, "fish eyes" or jells being formed in the product, and occasionally results in the process machine being starved by an insufficient supply of material.
In order to eliminate the accumulation of a large amount of scrap material in the common supply container at the extruder, the size of the common supply container in the past has been reduced so that it is impossible to accumulate a large supply of the scrap material; however, the reduction in volume of the common supply container is undesirable since, for instance, only a small amount of base material and scrap material can be maintained at the extruder, and the extruder is occasionally starved of either base material or scrap material when a low level of material in the common supply container is not discovered very quickly and compensated for.